Various autonomous devices have been developed that are configured to capture an image from within in vivo passages and cavities within a body, such as those passages and cavities within the gastrointestinal (GI) tract. These devices typically comprise a digital camera housed within a capsule along with light sources for illumination. The capsule may be powered by batteries or by inductive power transfer from outside the body. The capsule may also contain memory for storing captured images and/or a radio transmitter for transmitting data to an ex vivo receiver outside the body.
A common diagnostic procedure involves the patient swallowing the capsule, whereupon the camera begins capturing images and continues to do so at intervals as the capsule moves passively through the cavities made up of the inside tissue walls of the GI tract under the action of peristalsis. The capsule's value as a diagnostic tool depends on it capturing images of the entire interior surface of the organ or organs of interest. Unlike endoscopes, which are mechanically manipulated by a physician, the orientation and movement of the capsule camera are not under an operator's control and are solely determined by the physical characteristics of the capsule, such as its size, shape, weight, and surface roughness, and the physical characteristics and actions of the bodily cavity. Both the physical characteristics of the capsule and the design and operation of the imaging system within it must be optimized to minimize the risk that some regions of the target lumen are not imaged as the capsule passes through the cavity.
Two general image-capture scenarios may be envisioned, depending on the size of the organ imaged. In relatively constricted passages, such as the esophagus and the small intestine, a capsule which is oblong and of length less than the diameter passage, will naturally align itself longitudinally within the passage. Typically, the camera is situated under a transparent dome at one (or both) ends of the capsule. The camera faces down the passage so that the center of the image comprises a dark hole. The field of interest is the intestinal wall at the periphery of the image
The capsule 100 is encased in a housing 101 so that it can travel in vivo inside an organ 102, such as an esophagus or a small intestine, within an interior cavity 104. The capsule may be in contact with the inner surfaces 106, 108 of the organ, and the camera lens opening 110 can capture images within its field of view 112. The capsule may include an output port 114 for outputting image data, a power supply 116 for powering components of the camera, a memory 118 for storing images, image compression 120 circuitry for compressing images to be stored in memory, an image processor 122 for processing image data, and LEDs 126 for illuminating the surfaces 106, 108 so that images can be captured from the light that is scattered off of the surfaces.
It is desirable for each image to have proportionally more of its area to be intestinal wall and proportionally less the receding hole in the middle. Thus, a large FOV is desirable. A typical FOV is 140°. Unfortunately, a simple wide-angle lens will exhibit increased distortion and reduced resolution and numerical aperture at large field angles. High-performance wide-angle and “fish-eye” lenses are typically large relative to the aperture and focal length and consist of many lens elements. A capsule camera is constrained to be compact and low-cost, and these types of configurations are not cost effective. Further, these conventional devices waste illumination at the frontal area of these lenses, and thus the power use to provide such illumination is also wasted. Since power consumption is always a concern, such wasted illumination is a problem. Still further, since the intestinal wall within the filed of view extends away from the capsule, it is both foreshortened and also requires considerable depth of field to image clearly in its entirety. Depth of field comes at the expense of exposure sensitivity.
The second scenario occurs when the capsule is in a cavity, such as the colon, whose diameter is larger than any dimension of the capsule. In this scenario the capsule orientation is much less predictable, unless some mechanism stabilizes it. Assuming that the organ is empty of food, feces, and fluids, the primary forces acting on the capsule are gravity, surface tension, friction, and the force of the cavity wall pressing against the capsule. The cavity applies pressure to the capsule, both as a passive reaction to other forces such as gravity pushing the capsule against it and as the periodic active pressure of peristalsis. These forces determine the dynamics of the capsule's movement and its orientation during periods of stasis. The magnitude and direction of each of these forces is influenced by the physical characteristics of the capsule and the cavity. For example, the greater the mass of the capsule, the greater the force of gravity will be, and the smoother the capsule, the less the force of friction. Undulations in the wall of the colon will tend to tip the capsule such that the longitudinal axis of the capsule is not parallel to the longitudinal axis of the colon.
Also, whether in a large or small cavity, it is well known that there are sacculations that are difficult to see from a capsule that only sees in a forward looking orientation. For example, ridges exist on the walls of the small and large intestine and also other organs. These ridges extend somewhat perpendicular to the walls of the organ and are difficult to see behind. A side or reverse angle is required in order to view the tissue surface properly. Conventional devices are not able to see such surfaces, since their FOV is substantially forward looking. It is important for a physician to see all areas of these organs, as polyps or other irregularities need to be thoroughly observed for an accurate diagnosis. Since conventional capsules are unable to see the hidden areas around the ridges, irregularities may be missed, and critical diagnoses of serious medical conditions may be flawed. Thus, there exists a need for more accurate viewing of these often missed areas with a capsule.
FIG. 2 shows a relatively straightforward example where the passage 134, such as a human colon, is relatively horizontal, with the exception of the ridge 136, and the capsule sits on its bottom surface 132 with the optical axis of the camera parallel to the colon longitudinal axis. The ridge illustrates a problematic viewing area as discussed above, where the front surface 138 is visible and observable by the capsule 100 as it approaches the ridge. The backside of the capsule 140, however, is not visible by the capsule lens, as the limited FOV 110 does not pick up that surface. Specifically, the range 110 of the FOV misses part of the surface, and moreover misses the irregularity illustrated as polyp 142.
Three object points within the field of view 110 are labeled A, B, and C. The object distance is quite different for these three points, where the range of the view 112 is broader on one side of the capsule than the other, so that a large depth of field is required to produce adequate focus for all three simultaneously. Also, if the LED (light emitting diode) illuminators provide uniform flux across the angular FOV, then point A will be more brightly illuminated than point B and point B more than point C. Thus, an optimal exposure for point B results in over exposure at point A and under exposure at point C. For each image, only a relatively small percentage of the FOV will have proper focus and exposure, making the system inefficient. Power is expended on every portion of the image by the flash and by the imager, which might be an array of CMOS or CCD pixels. Moreover, without image compression, further system resources will be expended to store or transmit portions of images with low information content. In order to maximize the likelihood that all surfaces within the colon are adequately imaged, a significant redundancy, that is, multiple overlapping images, is required.
One approach to alleviating these problems is to reduce the instantaneous FOV but make the FOV changeable. Patent application 2005/0146644 discloses an in-vivo sensor with a rotating field of view. The illumination source may also rotate with the field of view so that regions outside the instantaneous FOV are not wastefully illuminated. This does not completely obviate the problem of wasteful illumination, and furthermore creates other power demands when rotating. Also, this innovation by itself does not solve the depth of field and exposure control problems discussed above.
Thus there exists a need in the art for a more improved system and method for in-vivo viewing of organs with a capsule, where better viewing angles can provide better observations of tissue surfaces. As will be seen below, the invention provides such a system and a method that overcomes the problems of the prior art, and they do so in an elegant manner.